One of current trends of development in the storage industry relates to methods and strategies for reduced energy consumption. Data centers may comprise nowadays dozens of storage systems, each comprising hundreds of disk drives. Clearly, most of the data stored in these systems is not in use for long periods of time, and hence most of the disks are likely to contain data that is not accessed for long periods of time. Power is unnecessarily spent in keeping all these disks spinning and, moreover, in cooling the data centers. Thus, efforts are now being invested in reducing energy-related spending in storage systems. Moreover, regulations are being increasingly enforced in many countries, forcing data centers to adopt “green” technologies for their servers and storage systems.
Some strategies have been developed for regulating energy use within the system, based on the possibility of transitioning the drives to a low-power state when they are not in use, and restoring the normal, or “active” state whenever needed.
Techniques that rely on the copying or migration of data can be referred to generally as “data-placing” techniques. For example, extra cache disks can be used to cache recently-accessed data while the original disks can remain mostly idle and, thus, in low-power mode.
Certain techniques are directed to classify data as “popular” or “unpopular” and rearrange and migrate different classes of data to separate sets of disks (or disk units) in such a way that utilization of data in the unpopular set is reduced, such that these disks can be transitioned to low-power mode.
References considered to be relevant as background to the presently disclosed subject matter are listed below. Acknowledgement of the references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.
US Patent application No. 2009/249001 (Narayanan et al.) discloses storage systems which use write off-loading. When a request to store some data in a particular storage location is received, if the particular storage location is unavailable, the data is stored in an alternative location. In one example, the particular storage location may be unavailable because it is powered down or because it is overloaded. The data stored in the alternative location may be subsequently recovered and written to the particular storage location once it becomes available.
U.S. Pat. No. 7,552,297 discloses a system and method directed to improve the efficiency of copy-on-write operations in a storage system. A PASS descriptor associated with partition PSS and a PDTT descriptor associated with partition PTT are maintained in a cache memory, with partition PSS associated with a source logical unit LUS and partition PTT associated with a source logical unit LUT. An ICP flag is set in the PDSS and PDTT descriptors indicating that the PSS and PTT are undergoing a copy-on-write operation. Data is then dissociated with PTT and locations of each block of the PSS stored in memory are copied from the PDSS descriptor to the PDTT descriptor. A task is then created to fetch blocks of the PSS and the fetched blocks are copied from the PSS to the PTT.